Limiting Magnitudes

[JohnP]

Hi All,

I have been trying to identify the limiting Mag of my recent M81 image. SkyMap Pro seems to only go to about Mag 15 so was just wondering if anyone lnew any free s/W or other s/W that goes lower & if so how low..? I have attached an inverted image of my m81 & ringed the stars I'm trying to identify. Any help would be greatly appreciated.

Thks,  John

[Mike]

John - Does SkyMap allow you to load in more catalogues? If so, just load in a catalogue that goes much deeper like USNO which I believe goes down to Mag 21.

[MarkS]

John, do what I do and use astrometry - IRIS will do it quite happily.  Just calibrate it to stars whose magnitude you know then you can select any other star and it'll tell you the magnitude.

[RobertM]

Hi John,

From The Sky,  the magnitudes of those starts you've circled are:

Top Left : 17.77
Middle left : 16.3
Bottom right : 18.14

I tried to paste the image to get the magnitudes of all the stars but that wouldn't work so hope the above is ok.

Cheers
Robert

[JohnP]

Thks guys... that helps.

You can use external catalogs with SMP but it doesn't like large ones & USNO is something like 6Gb. I've just downloaded Cartes Du Ciel which can use professional external cats - i'm trying to figure out how download the extra catalogs..

Mark - I'm also trying to do some Photometry (or is it Astrometry) in AIP4WIN & will let you know.

Robert - Thks for that - once I've got some numbers I'll see how they compare with yours.

Thks again,   John

[Rick]

Photometry (or is it Astrometry)

Photometry - measuring the light (magnitude, spectrum, ...)

Astrometry - measuring the position and motion

[MarkS]

Astrometry? Photometry?

"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less"

[JohnP]

OK - I eventually got round to doing some Photometry on my m81 image... Found a great website:

http://www.aavso.org/observing/charts/vsp/

You can put in the RA & DEC for an area of sky you are interested in & then choose a size (say 25 arcmins) & it will either plot or use a DSS image & give photometrically correct magns of stars (great to use for ref against your own images). I also used the single star photometry tool on AIP4Win. Anyway I've annotated some of the known mags on my image. The faintest mag I could measure was approx 19.5 to 20 on this image which isn't bad for 4min subs - be interesting to do same at DSC.

Anyway image is here:

Cheers,  John

[MarkS]

That's a lovely image John and I like your work on the limiting magnitudes.